The present invention relates to a sampling device for taking a water sample under pressure deep in a bore hole made in the earth.
Especially in investigations to determine the suitability of bed rock as a final place of storage for nuclear waste, it is necessary to obtain accurate information about the conditions prevailing inside the rock. Such information is obtained via hydrochemical analysis of water obtained from a hole bored in the rock.
In such cases, the holes are usually at least several hundreds of meters deep and the conditions deep in the hole are completely different from those on the ground surface. Therefore, a water sample pumped up from the hole to the ground surface no longer corresponds to a water sample deep in the hole, but, especially due to the pressure difference, the gases dissolved in the water under a high pressure are largely separated from the aqueous phase at normal air pressure.
In prior art, in an attempt to eliminate these problems, use has been made of a container in which a vacuum is created while on the ground. The container is then lowered deep into the hole, where it is filled through a valve. The container keeps the water sample at the pressure prevailing at the sampling depth, so the liquid can be studied in this pressurized state. However, this structure involves significant problems. When the container previously exhausted on the ground is filled, the water pressure falls radically and the dissolved gases may be separated from the aqueous phase. Maintaining the pressure while the container is being hoisted up is a further problem.
The object of investigation is natural water present in chinks in the rock, but the water obtained from a hole hardly ever represents it accurately. Even from rock chinks, a sample close to the natural condition can only be obtained after prolonged pumping.
Further problems in performing the measurements are also caused by the relatively small hole diameter of .0. 56 mm generally used in these investigations. Such holes cannot accommodate very complicated equipment.